1. Field of the Invention
This invention relates generally to apparatus and methods for designing micro-electromechanical system (MEMS) based optical and photonic devices for fiber optical transmission systems. More particularly, this invention is related to the optimization of the configuration of optical and photonic tunable devices based on Fabry-Perot theory such as variable optical attenuator (VOA), tunable filter, optical switch, dynamic dispersion compensator, etc., for use in optical communication sub-system or system.
2. Description of the Related Art
Even with recent advancements made in the MEMS technologies to produce optical devices with low power consumption, small size, high speed and reliability, the designs, manufacture and package of the tunable MEMS devices based on Fabry-Perot principle are still faced with a very demanding technical challenge. Specifically, since the performances of a Fabry-Perot based tunable optical device is determined by the structure of the membranes and the gap between the membranes, different tunable optical devices generally use different membranes and different control circuits for controlling and tuning the gaps between the membranes of these optical devices. Accordingly, different MEMS optical devices are made with different size and structural features each controlled by different control circuits having different packages. There is a lack of standard basic device structure and control methodology for the Fabry-Perot based tunable MEMS devices. The production costs, product reliability and device performance are adversely affected due to the lack of standard structural and device tuning configurations.
Based on the well known Fabry-Perot interferometer constructed by Charles Fabry and Alfred Perot, Goossen discloses in U.S. Pat. Nos. 5,943,155 and 5,949,571, entitled xe2x80x9cMARS Optical Modulatorxe2x80x9d a resonator formed with membrane supported on a silicon substrate. The device is made with surface micro-electro-machining process. The membrane of the resonator is tuned electronically to provide an electrically tunable modulator. Goosen""s modulator as disclosed has several technical limitations. One co-pending patent application filed by some of the co-inventors of this Application, MEMS based variable optical attenuator, and a to-be filed patent, MEMS based tunable optical filter, disclose further improvement for manufacturing variable optical attenuators (VOA) and tunable optical filter to overcome Goossn""e limitations. The co-pending Patent Application are hereby incorporated by reference in this Application. The co-pending Applications provide mass producible tunable MEMS device with improved performance. However, there is still a demand for standard MEMS device structure assembled with simplified configuration while tunable with a single control circuit for a standard tuning cavity such that the manufacturing processes and configuration can be conveniently employed for producing different kinds of optical devices.
A need still exists in the art in the field of the optical signal transmission systems to provide an optimized design and configuration to manufacture an universal basic tunable device structure controllable by a single standard control configuration in order to overcome the difficulties and limitations now encountered in the prior art. It is further desirable that different devices are designed to be controllable by a single smart control circuit. One smart control circuit is able to compensate different environmental factors such as temperature variations for different types of optical devices so that a selected wavelength, attenuation or dispersion value, according to device designs can be fixed without substantial impact due to variations of environmental conditions.
It is the object of the present invention to provide a new design and manufacture method for producing tunable optical devices with novel tuning configuration implemented with a separate and universal tuning cavity. This separate universal tuning cavity can be implemented in different kinds of tunable optical devices with standard control circuit. Therefore, this invention discloses a standard configuration for MEMS based tunable optical devices to overcome the limitations and difficulties as discussed above for the prior art techniques.
Specifically, it is an object to the present invention to provide a new design and manufacture method for producing tunable optical devices with a standard dual cavity configuration includes a performance cavity based on device design specifications and a tuning cavity for tuning the optical device embodied in the performance cavity. The tuning cavity is designed to have tuning ranges suitable for different kinds of optical devices to be embodied in the performance cavity. Therefore, the tuning cavity can be universally implemented to a wide varieties of tunable MEMS based optical devices with a single standardized control circuit for tuning and controlling different types of tunable optical devices with reduced production costs and higher performance and improved device reliability.
Another object of the invention is to present a new design and manufacture method for producing tunable optical devices with a standard dual cavity configuration includes a performance cavity and a tuning cavity. The performance cavity includes two membranes wherein the shape, size and gap between the membranes are based on device design specifications and these two membranes may be simultaneously produced by identical set of silicon-based MEMS manufacturing processes such that the optical loss of the performance can be optimally reduced for particular optical devices while for other devices, such as dispersion compensation device, two different membranes are provided.
Another object of the invention is to present a new design and manufacture method for producing tunable optical devices with a standard dual cavity configuration includes a performance cavity and a tuning cavity. The performance cavity includes two membranes wherein the membranes are formed with multiple layers to increase the refraction rates and the membranes further include non-conductive areas to reduce optical loss and achieve higher resonating performance.
Another object of the invention is to present a new design and manufacture method for producing tunable optical devices with a standard dual cavity configuration includes a performance cavity and a tuning cavity. The performance of the optical device is further improved by using a 100% reflection mirror to re-direct the light beam and by causing the light passing twice through the performance cavity functioning as a resonator. The residual basic mode of MEMS resonator is designed to match the input light mode. In one preferred embodiment performance cavity is formed with parallel structure to achieve very low insertion loss without the match of the basic resonator residual mode and a specified incident beam mode.
Another object of the invention is to present a new design and manufacture method for producing tunable optical devices with a standard dual cavity configuration includes a performance cavity and a tuning cavity. In the tuning cavity, the electrodes for tuning are formed as face-to-face conductive layers with no dielectric between the conductive layer, so that no material traps the charges between the positive and negative electrodes. An electronic control circuit with temperature and wavelength compensation functionality makes the tunable MEMS device to function with stability at the tuned wavelength without variation when the temperature changes.
Specifically, this invention discloses a tunable optical device is disclosed. The tunable optical device includes a tuning cavity having a tuning means provided for alternately bonding to at least two different tunable optical cells each comprising a tuning membrane wherein the tuning cavity disposed near the tuning membrane for moving the tuning membrane for tuning one of the at least two tunable optical cells bonded thereon. In a preferred embodiment, the tuning cavity further includes a first electrode disposed on the tuning membrane and a second electrode disposed on a substrate supporting the tuning cavity for applying a voltage to move the tuning membrane. In a preferred embodiment, the optical device further includes an optical device control circuit connected to the tuning means for controlling and moving the tuning membrane. In a preferred embodiment, the tuning cavity further includes through hole along an optical path for an optical transmission passing through the tunable membrane for providing an interface-free and ripple-free optical path for the optical transmission. In a preferred embodiment, the tunable optical cells constitute an optical filter for bonding to the tuning cavity and tunable by moving the tunable membrane. In a preferred embodiment, the tunable optical cells constitute an optical attenuator for bonding to the tuning cavity and tunable by moving the tunable membrane. In a preferred embodiment, the tunable optical cells constitute an optical switch for bonding to the tuning cavity and tunable by moving the tunable membrane. In a preferred embodiment, the tunable optical cells constitute an optical dispersion compensator for bonding to the tuning cavity and tunable by moving the tunable membrane. In a preferred embodiment, the optical device constitutes a micro-electro-mechanical system (MEMS) optical device manufactured by applying a micro-electro-mechanical system (MEMS) technology.
Briefly, this invention discloses a method for configuring a tunable optical device. The method includes a step of forming a tuning cavity by providing a tuning means for alternately bonding one of at least two different tunable optical cells each comprising a tuning membrane and disposing the tuning cavity near the tuning membrane for moving the tuning membrane for tuning one of the at least two tunable optical cells bonded thereon. In a preferred embodiment, the step of forming the tuning cavity further includes a step of disposing a first electrode on the tuning membrane and disposing a second electrode on a substrate supporting the tuning cavity for applying a voltage to move the tuning membrane. In a preferred embodiment, the method further includes a step of connecting an optical device control circuit to the tuning means for controlling and moving the tuning membrane. In a preferred embodiment, the step of forming the tuning cavity further includes a step of opening a through hole in the tuning cavity along an optical path for an optical transmission passing through the tunable membrane for providing an interface-free and ripple-free optical path for the optical transmission. In a preferred embodiment, the step of alternately bonding the one of at least two different types of tunable optical cells further comprise a step of bonding an optical filter to the tuning cavity. In a preferred embodiment, the step of alternately bonding the one of at least two different types of tunable optical cells further comprise a step of bonding an optical attenuator to the tuning cavity. In a preferred embodiment, the step of alternately bonding the one of at least two different types of tunable optical cells further comprise a step of bonding an optical switch to the tuning cavity. In a preferred embodiment, the step of alternately bonding the one of at least two different types of tunable optical cells further comprise a step of bonding an optical dispersion compensator to the tuning cavity. In a preferred embodiment, the step of alternately bonding the one of at least two different types of tunable optical cells to the tunable cavity further comprising a step of applying a micro-electro-mechanical system (MEMS) technology for manufacturing and bonding the one of at least two different types of tunable optical cells to the tunable cavity.
These new configurations produce an optical tunable device with low insertion loss, low polarization dependent loss, low temperature-dependent loss (TDL), high performance ripple free, larger fineness or larger tuning attenuation range. The present invention also provides a device configuration with relatively large tolerances of manufacturing process-deviations hence significantly reduces the production cost.